Policeman stand guard outside the King Edward VII hospital where the Duchess of Cambridge has been admitted with a severe form of morning sickness, in London, Monday, Dec. 3, 2012. Prince William and his wife Kate are expecting their first child. St. James's Palace announced the pregnancy Monday, saying that the Duchess of Cambridge — formerly known as Kate Middleton — has a severe form of morning sickness and is currently in a London hospital. William is at his wife's side. The palace said since the pregnancy is in its "very early stages," the 30-year-old duchess is expected to stay in the hospital for several days and will require a period of rest afterward. (AP Photo/Alastair Grant)

Britain's Prince William and Kate Duchess of Cambridge pass along The Mall as part of a four-day Diamond Jubilee celebration to mark the 60th anniversary of Queen Elizabeth's accession to the throne, London, Tuesday, June, 5, 2012. (AP Photo/Tom Hevezi, Pool)

Britain's Prince William and his wife Kate, the Duke and Duchess of Cambridge, smile as they watch a shark ceremony as they arrive at Marapa Island, Solomon Islands, Monday, Sept. 17, 2012. (AP Photo/Rick Rycroft, Pool)

Photo: Rick Rycroft, Associated Press

Britain's Prince William and his wife Kate, the Duke and Duchess of...

Britain's Prince William and his wife Kate, the Duke and... Photo-3838441.53358 - SFGate

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Britain's Kate, the Duchess of Cambridge, smiles as she and Prince William prepare to depart Honiara, Solomon Islands, Tuesday, Sept. 18, 2012, after an official visit to the South Pacific Island nation. (AP Photo/Rick Rycroft)

Photo: Rick Rycroft, Associated Press

Britain's Kate, the Duchess of Cambridge, smiles as she and Prince...

Britain's Kate, the Duchess of Cambridge, smiles as she and... Photo-3838436.53358 - SFGate

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Kate, the Duchess of Cambridge, plays hockey during her visit to St. Andrew's School, where she attended school from 1986 till 1995, in Pangbourne, England, Friday, Nov. 30, 2012. The Duchess of Cambridge has gone back to school. The royal, formerly known as Kate Middleton, played hockey and revealed her childhood nickname — Squeak — when she returned to her elementary school for a visit Friday. Kate told teachers and students at the private St. Andrew's School in southern England that her 10 years there were "some of my happiest years." She said that she enjoyed it so much that she had told her mother she wanted to return as a teacher. (AP Photo/Arthur Edwards, Pool)

(FILE PHOTO) St James's Palace has announced that Prince William and Catherine Duchess Of Cambridge are expecting a baby LONDON - FEBRUARY 10: Prince Harry (L) and Prince William (C) and Kate Middleton (R)cheer on the English team during the RBS Six Nations Championship match between England and Italy at Twickenham on February 10, 2007 in London, England. (Photo by Richard Heathcote/Getty Images)

(FILES) - A picture dated November 16, 2010 shows Britain's Prince William (R) and his fiance Kate Middleton posing for photographers during a photocall to mark their engagement, in the State Rooms of St James Palace, central London. Prince William's wife Catherine is pregnant with their first child, St James's Palace said on December 3, 2012, in an eagerly awaited announcement about a baby destined to be Britain's future king or queen. AFP PHOTO/BEN STANSALLBEN STANSALL/AFP/Getty Images

FILE - In this Friday April 29, 2011 file photo Britain's Prince William and his bride Kate, Duchess of Cambridge, leave Westminster Abbey, London, following their wedding. The Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting a baby, St James's Palace officially announced Monday Dec. 3, 2012. (AP Photo/Tom Hevezi, File)

FILE - In this Thursday, Sept. 13, 2012 file photo, Kate, the Duchess of Cambridge visits the Kranji Commonwealth War Memorial in Singapore. Prince William and his wife Catherine are expecting their first child. St. James's Palace announced the pregnancy Monday, saying that the Duchess of Cambridge, formerly known as Kate Middleton has a severe form of morning sickness and is currently in a London hospital. William is at his wife's side. (AP Photo/Nicolas Asfouri, Pool, File)

Kate Middleton (L) waves as she arrives with her sister, the Maid of Honour Philippa Middleton at the West Door of Westminster Abbey in London for her wedding to Britain's Prince William, on April 29, 2011. AFP PHOTO / BEN STANSALL (Photo credit should read BEN STANSALL/AFP/Getty Images)

Photo: Ben Stansall

Kate Middleton (L) waves as she arrives with her sister, the Maid...

Kate Middleton (L) waves as she arrives with her sister, the Maid... Photo-3838444.53358 - SFGate